That helmet was a real design that was being considered by the team. It was proposed in 1990, but they thought it was too radical of a change to have the team adopt.
Here are some other unique helemts you may or may not have seen:
This Falcons helmet was proposed in 2002 and never accepted.
The Baltimore Bombers were not a name being considered when the Browns moved and became the Ravens. However, the Bombers were one of the teams competing for a team that eventually went to Carolina and Jacksonville.
Was considered, but never changed.
One idea that was passed around for the Lions.
Ron Wolf proposed this color change for the Packers in 1990, but they figured fans would be too upset.
Original Houston Texans helmet.
Jaguars prototype.
The Memphis Hound Dogs was one of five teams competitng to be an NFL team.
Carmen Policy actually changed the helmets to this in 1991, but it was changed back 24 hours after he introduced it to the public because of fan's outcries.
The St. Louis Stallions were the 5th team that competed against the Hound Dogs, Bombers, Jaguars and Panthers.